Challenge Mode
Challenge Mode is the final extra mode you unlock (at the time of writing) and is available upon upgrading the Command Center to level 5 and is also the most recent addition to the game along with the Perk System which is directly associated with this mode. Challenge mode is just what it is. A Challenge. In this mode, your own unit's powers, base upgrades, or resources have no effect on the gameplay. Just plain luck.
Every 24 hours, you are given a mixed set of units. Type of units, number, upgrade level are all random. Choose five types of units among the whole random bunch. They can be a mix of all production structures. Even those you haven't built yet.
The Heroes that are provided to you are the same as well. Choose from three heroes among the 5 given at random. The level of their skills are also randomized. You have to fully select your team to be able to continue and play the mode.
Once the team has been assembled, a selection of stages with increasing difficulty and rewards will be available from left to right. These stages are entirely RANDOM. You must make your way over to the very end. Doing so also yields greater rewards. However this isn't a simple task since all your units are random and you must manage to tackle on complex bases with the random units and Heroes given to you.
Once a unit or hero dies, they are considered "depleted resources" and can no longer be used in further stages or in the same stage if you fail in completing the stage so be careful upon deploying units. The Skill Points given is also fixed and further skill points to be used will only be through acquisition from Buildings destroyed so use the points wisely.